Parkinsonism in cirrhosis: pathogenesis and current therapeutic options

Manganese efflux transporter SLC30A10 missense polymorphism T95I associated with liver injury retains manganese efflux activity

The activity of the manganese (Mn) efflux transporter SLC30A10 in the liver and intestines is critical for Mn excretion and preventing Mn toxicity. Homozygous loss-of-function mutations in SLC30A10 are a well-established cause of hereditary Mn toxicity. But, the relationship between more common SLC30A10 polymorphisms, Mn homeostasis, and disease is only recently emerging. In 2021, the first coding SNP in SLC30A10 (T95I) was associated with liver disease raising the hypothesis that the T95I substitution may induce disease by inhibiting the Mn efflux function of SLC30A10. Here, we test this hypothesis using structural, viability, and metal quantification approaches. Analyses of a predicted structure of SLC30A10 revealed that the side chain of T95 pointed away from the putative Mn-binding cavity, raising doubts about the impact of the T95I substitution on SLC30A10 function. In HeLa or HepG2 cells, overexpression of SLC30A10-WT or T95I resulted in comparable reductions of intracellular Mn levels and protection against Mn-induced cell death. Furthermore, ΔSLC30A10 HepG2 cells, generated using CRISPR/Cas9, exhibited elevated Mn levels and heightened sensitivity to Mn-induced cell death, and these phenotypic changes were similarly rescued by expression of SLC30A10-WT or T95I. Finally, turnover rates of SLC30A10-WT or T95I were also comparable. In summary, our results indicate that the Mn transport activity of SLC30A10-T95I is essentially comparable to the WT protein. Our findings imply that SLC30A10-T95I either has a complex association with liver injury that extends beyond the simple reduction in SLC30A10 activity or alternatively the T95I mutation lacks a causal role in liver disease.NEW & NOTEWORTHY This study demonstrates that the T95I polymorphism in the manganese transporter SLC30A10, which has been associated with liver disease in human GWAS studies, does not impact transporter function in cell culture. These findings raise doubts about the causal relationship of the T95I polymorphism with human disease and highlight the importance of validating GWAS findings using mechanistic approaches.

The Combined Inactivation of Intestinal and Hepatic ZIP14 Exacerbates Manganese Overload in Mice

ZIP14 is a newly identified manganese transporter with high levels of expression in the small intestine and the liver. Loss-of-function mutations in ZIP14 can lead to systemic manganese overload, which primarily affects the central nervous system, causing neurological disorders. To elucidate the roles of intestinal ZIP14 and hepatic ZIP14 in maintaining systemic manganese homeostasis, we generated mice with single-tissue or two-tissue Zip14 knockout, including intestine-specific (Zip14-In-KO), liver-specific (Zip14-L-KO), and double (intestine and liver) Zip14-knockout (Zip14-DKO) mice. Zip14^flox/flox mice were used as the control. Tissue manganese contents in these mice were compared using inductively coupled plasma mass spectrometry (ICP-MS) analysis. We discovered that although the deletion of intestinal ZIP14 only moderately increased systemic manganese loading, the deletion of both intestinal and hepatic ZIP14 greatly exacerbated the body's manganese burden. Our results provide new knowledge to further the understanding of manganese metabolism, and offer important insights into the mechanisms underlying systemic manganese overload caused by the loss of ZIP14.

Acquired Hepatocerebral Degeneration After a Splenorenal Shunt in the Sub-Saharan Africa Context: A Case Report and Brief Review of Literature

Acquired hepatocerebral degeneration (AHD) is a neurologic syndrome caused by liver dysfunction and long-standing portosystemic shunting. The pathogenesis of the condition is predominantly considered to be related to the deposition of manganese in parts of the brain due to shunting. We report a case of a 25-year-old male who underwent splenectomy and splenorenal shunt for recurrent upper GI bleeding (UGIB) due to esophageal varices caused by non-cirrhotic portal hypertension (NCPH). He presented with bradykinesia, hypophonia, gait instability, and rigidity of the lower extremities 18 months after the procedure was done.

Up-regulation of the manganese transporter SLC30A10 by hypoxia-inducible factors defines a homeostatic response to manganese toxicity

Manganese (Mn) is an essential metal that induces incurable parkinsonism at elevated levels. However, unlike other essential metals, mechanisms that regulate mammalian Mn homeostasis are poorly understood, which has limited therapeutic development. Here, we discovered that the exposure of mice to a translationally relevant oral Mn regimen up-regulated expression of SLC30A10, a critical Mn efflux transporter, in the liver and intestines. Mechanistic studies in cell culture, including primary human hepatocytes, revealed that 1) elevated Mn transcriptionally up-regulated SLC30A10, 2) a hypoxia response element in the SLC30A10 promoter was necessary, 3) the transcriptional activities of hypoxia-inducible factor (HIF) 1 or HIF2 were required and sufficient for the SLC30A10 response, 4) elevated Mn activated HIF1/HIF2 by blocking the prolyl hydroxylation of HIF proteins necessary for their degradation, and 5) blocking the Mn-induced up-regulation of SLC30A10 increased intracellular Mn levels and enhanced Mn toxicity. Finally, prolyl hydroxylase inhibitors that stabilize HIF proteins and are in advanced clinical trials for other diseases reduced intracellular Mn levels and afforded cellular protection against Mn toxicity and also ameliorated the in vivo Mn-induced neuromotor deficits in mice. These findings define a fundamental homeostatic protective response to Mn toxicity-elevated Mn levels activate HIF1 and HIF2 to up-regulate SLC30A10, which in turn reduces cellular and organismal Mn levels, and further indicate that it may be possible to repurpose prolyl hydroxylase inhibitors for the management of Mn neurotoxicity.

Acquired hepatocerebral degeneration in a metastatic neuroendocrine tumor long-term survivor — an update on neuroendocrine neoplasm’s treatment: A case report

BACKGROUND

Metastatic small bowel low-grade neuroendocrine tumors (NETs) have a good prognosis. Surgery is the only curative treatment; however, this may induce advanced liver disease, particularly in long-term survivor patients. Acquired hepatocerebral degeneration or Parkinsonism in cirrhosis is characterized by rapidly progressive extrapyramidal symptoms in patients with advanced liver disease.

CASE SUMMARY

A 70-year-old man presented to the emergency department with diminished consciousness and disorientation, and was diagnosed with hepatic encephalopathy. The patient was diagnosed in 1993 with a metastatic small bowel NET, for which he twice underwent hepatic surgery, with metastatic resection in 1993 and a right hepatectomy in 2002 to remove two hepatic metastases. In 2003, the patient started first-line chemotherapy and in 2004 started the first of three consecutive biological treatments, followed by radio-molecular therapy, achieving stable disease for 14 years. Disease progression was identified and he underwent an endoscopic retrograde cholangiopancreatography. However, in 2019 advanced liver disease was identified. We diagnosed the development of acquired hepatocerebral degeneration, an unusual long-term side effect after multiple hepatic procedures.

CONCLUSION

The importance of regular and ongoing surveillance in long-term NET survivors who undergo hepatic procedures should be integrated into the therapeutic management plan, as some of these negative outcomes could be prevented.

Alpha-Synuclein in Alcohol Use Disorder, Connections with Parkinson's Disease and Potential Therapeutic Role of 5' Untranslated Region-Directed Small Molecules

Alpha-synuclein (α-Syn) is a 140-amino acid (aa) protein encoded by the Synuclein alpha SNCA gene. It is the synaptic protein associated with Parkinson's disease (PD) and is the most highly expressed protein in the Lewy bodies associated with PD and other alpha synucleopathies, including Lewy body dementia (LBD) and multiple system atrophy (MSA). Iron deposits are present in the core of Lewy bodies, and there are reports suggesting that divalent metal ions including Cu2+ and Fe2+ enhance the aggregation of α-Syn. Differential expression of α-Syn is associated with alcohol use disorder (AUD), and specific genetic variants contribute to the risk for alcoholism, including alcohol craving. Spliced variants of α-Syn, leading to the expression of several shorter forms which are more prone to aggregation, are associated with both PD and AUD, and common transcript variants may be able to predict at-risk populations for some movement disorders or subtypes of PD, including secondary Parkinsonism. Both PD and AUD are associated with liver and brain iron dyshomeostasis. Research over the past decade has shown that α-Syn has iron import functions with an ability to oxidize the Fe3+ form of iron to Fe2+ to facilitate its entry into cells. Our prior research has identified an iron-responsive element (IRE) in the 5' untranslated region (5'UTR) of α-Syn mRNA, and we have used the α-Syn 5'UTR to screen for small molecules that modulate its expression in the H4 neuronal cell line. These screens have led us to identify several interesting small molecules capable of both decreasing and increasing α-Syn expression and that may have the potential, together with the recently described mesenchymal stem cell therapies, to normalize α-Syn expression in different regions of the alcoholic and PD brain.

Spontaneous portosystemic shunts in liver cirrhosis: new approaches to an old problem

Portal hypertension is the main consequence of liver cirrhosis, leading to severe complications such as variceal hemorrhage, ascites or hepatic encephalopathy. As an attempt to decompress the portal venous system, portal flow is derived into the systemic venous system through spontaneous portosystemic shunts (SPSSs), bypassing the liver. In this review, we aim to provide an overview of the published reports in relation to the prevalence and physiopathology behind the appearance of SPSS in liver cirrhosis, as well as the complications derived from its formation and its management. The role of SPSS embolization is specifically discussed, as SPSSs have been assessed as a therapeutic target, mainly for patients with recurrent/persistent hepatic encephalopathy and preserved liver function. Furthermore, different aspects of the role of SPSS in liver transplantation, as well as in candidates for transjugular intrahepatic portosystemic shunt are reviewed. In these settings, SPSS occlusion has been proposed to minimize possible deleterious effects, but results are so far inconclusive.

Manganese, a Likely Cause of 'Parkinson's in Cirrhosis', a Unique Clinical Entity of Acquired Hepatocerebral Degeneration

With idiopathic Parkinson's disease being a common entity, parkinsonism in acquired hepatocerebral degeneration (AHD) in the context of Manganese (Mn) has gained importance in recent years. An insight into the pathomechanisms behind this disease has been put forth. How can Mn as a divalent metal exert its effect in leading to chronic neurodegenerative disorder? Secondary to decreased excretion in liver cirrhosis, Mn significantly alters the striatal dopaminergic system. Management of this debilitating disease also focuses on different aspects where Mn has been involved in the pathogenesis. We have put forth the details behind Mn effects in Parkinson’s, which will be a guide for better understanding and management of this disease.

A literature search was performed using PubMed as a sole database, and all the articles were peer-reviewed. The author tried to follow the PRISMA guidelines. Inclusion criteria were set for 10 years, with most studies with in the last seven years. All types of study designs were included relevant to the topic, clearly delineating the pathomechanisms of Mn in the disease and also its management. After extensive research, through the PubMed database, we found that Parkinson's disease is one of the neurological complications in advanced liver cirrhosis. Mn is an essential element behind its pathogenesis; it works at different cellular levels to promote neurotoxicity. From its influx to its effects on dopamine transporters (DAT), where it disrupts dopamine homeostasis also altering postsynaptic dopamine (D2) receptors, it disrupts mitochondria and the endoplasmic reticulum (ER) promotes oxidative stress and neuroinflammation. Misfolding of alpha-synuclein (α-Syn) is promoted on chronic exposure to Mn where α-Syn from being neuroprotective becomes neurotoxic. It also alters glutaminergic and gabaergic neurotransmission. In a nutshell, the diversity of its effect on nigrostriatal denervation is challenging. The importance of neuroimaging and various approaches to management is also discussed. AHD, an uncommon entity in advanced liver cirrhosis, needs more awareness so that it can be diagnosed earlier and better therapeutic options can be sought. Our study highlighted Mn mechanisms behind this clinical entity, putting forth grounds for a better understanding of this disease. Advanced research targeting Mn for managing this disease will be revolutionary.

Maintaining Translational Relevance in Animal Models of Manganese Neurotoxicity

Manganese is an essential metal, but elevated brain Mn concentrations produce a parkinsonian-like movement disorder in adults and fine motor, attentional, cognitive, and intellectual deficits in children. Human Mn neurotoxicity occurs owing to elevated exposure from occupational or environmental sources, defective excretion (e.g., due to cirrhosis), or loss-of-function mutations in the Mn transporters solute carrier family 30 member 10 or solute carrier family 39 member 14. Animal models are essential to study Mn neurotoxicity, but in order to be translationally relevant, such models should utilize environmentally relevant Mn exposure regimens that reproduce changes in brain Mn concentrations and neurological function evident in human patients. Here, we provide guidelines for Mn exposure in mice, rats, nematodes, and zebrafish so that brain Mn concentrations and neurobehavioral sequelae remain directly relatable to the human phenotype.

How to approach a patient with parkinsonism - red flags for atypical parkinsonism

Parkinsonism is a clinical syndrome defined by bradykinesia plus rigidity or tremor. Though most commonly encountered in the setting of idiopathic Parkinson's disease, a number of neurodegenerative, structural, metabolic and toxic neurological disorders can result in parkinsonism. Accurately diagnosing the underlying cause of parkinsonism is of both therapeutic and prognostic relevance, especially as we enter the era of disease-modifying treatment trials for neurodegenerative disorders. Being aware of the wide array of potential causes of parkinsonism is of paramount importance for clinicians. In this chapter, we present a pragmatic clinical approach to patients with parkinsonism, specifically focusing on 'red flags', which should alert one to consider diagnoses other than idiopathic Parkinson's disease.

Pathophysiology of hepatic encephalopathy and future treatment options

Understanding of the pathophysiology of hepatic encephalopathy has conditioned new treatment options. Ammonia detoxification in hepatic encephalopathy is regulated by two enzymes: glutaminase or glutamine synthetase. The first produces ammonia and the second detoxifies the ammonia, which is why treatments are aimed at glutaminase inhibition or glutamine synthetase activation. At present, we know that both enzymes are found not only in the liver, but also in the muscle, intestine, kidney, and brain. Therefore, current treatments can be directed at each enzyme at different sites. Awareness of those potential treatment sites makes different options of approach possible in the patient with hepatic encephalopathy, and each approach should be personalized.

Hepatitis B and C virus infection as a risk factor for Parkinson's disease in Israel-A nationwide cohort study

OBJECTIVE

To study the association between hepatitis C and B viruses and Parkinson's disease (PD) in Israel.

METHODS

A retrospective cohort study was performed by analyzing the computerized database of Clalit Healthcare Service in Israel. Cohorts of people with hepatitis C virus (HCV) infection, hepatitis B virus (HBV) infection and nonalcoholic steatohepatitis (NASH) were constructed and compared to a reference cohort for prevalence of PD.

RESULTS

The prevalence of PD in Israel was found to be 0.5% in the general population. The M-H (Mantel-Haenszel) odds ratio (OR) of PD for HBV-positive patients was 1.08 (95% CI: 1.00-1.16). The M-H OR of PD for HCV-positive patients was 1.18 (95% CI: 1.04-1.35). The M-H OR of PD for patients infected with both hepatitis C and B was 1.13 (95% CI: 0.87-1.47). The M-H OR of PD for patients diagnosed with nonalcoholic steatohepatitis (NASH) was 1.13 (95% CI: 1.08-1.19).

CONCLUSIONS

We report evidence supporting a minor increased risk for PD in patients with HCV. Co infection of HCV and HBV was not associated with an increased risk for PD. The increased risk for PD in the group of patients with NASH, raises the possibility that liver disease per se is a risk factor for PD rather than viral infection. In addition, it cannot be ruled out that the association is, at least in part, the result of the occurrence of cirrhosis induced parkinsonism that was misclassified as PD.

Implications of Manganese in Chronic Acquired Hepatocerebral Degeneration

Neurological symptoms can be one of the over-riding symptoms in patients with liver cirrhosis. Patients can present with subtle changes in mood or neurological function due to hepatic encephalopathy (HE), to more severe presentations including stupor and coma. While HE, in its severe form, can be clinically easy to diagnose, more subtle forms may be more difficult to recognize. Other neurological diseases may indeed be overlooked in the context of cirrhosis or confuse the physician regarding the diagnosis. Chronic acquired hepatocerebral degeneration (CAHD) is an uncommon problem occurring in patients with cirrhosis characterised by a Parkinsonian-like neurological presentation with damage to the brain secondary to manganese (Mn) deposition. Here we describe a case of a patient with a neurological presentation of liver disease with a review of the current CAHD literature. In conclusion, CAHD is a rare condition occurring in liver cirrhosis that should always be considered in patients with neurological manifestations of chronic liver disease.

SLC30A10 transporter in the digestive system regulates brain manganese under basal conditions while brain SLC30A10 protects against neurotoxicity

The essential metal manganese becomes neurotoxic at elevated levels. Yet, the mechanisms by which brain manganese homeostasis is regulated are unclear. Loss-of-function mutations in SLC30A10, a cell surface-localized manganese efflux transporter in the brain and liver, induce familial manganese neurotoxicity. To elucidate the role of SLC30A10 in regulating brain manganese, we compared the phenotypes of whole-body and tissue-specific Slc30a10 knockout mice. Surprisingly, unlike whole-body knockouts, brain manganese levels were unaltered in pan-neuronal/glial Slc30a10 knockouts under basal physiological conditions. Further, although transport into bile is a major route of manganese excretion, manganese levels in the brain, blood, and liver of liver-specific Slc30a10 knockouts were only minimally elevated, suggesting that another organ compensated for loss-of-function in the liver. Additional assays revealed that SLC30A10 was also expressed in the gastrointestinal tract. In differentiated enterocytes, SLC30A10 localized to the apical/luminal domain and transported intracellular manganese to the lumen. Importantly, endoderm-specific knockouts, lacking SLC30A10 in the liver and gastrointestinal tract, had markedly elevated manganese levels in the brain, blood, and liver. Thus, under basal physiological conditions, brain manganese is regulated by activity of SLC30A10 in the liver and gastrointestinal tract, and not the brain or just the liver. Notably, however, brain manganese levels of endoderm-specific knockouts were lower than whole-body knockouts, and only whole-body knockouts exhibited manganese-induced neurobehavioral defects. Moreover, after elevated exposure, pan-neuronal/glial knockouts had higher manganese levels in the basal ganglia and thalamus than controls. Therefore, when manganese levels increase, activity of SLC30A10 in the brain protects against neurotoxicity.

Hypothyroidism induced by loss of the manganese efflux transporter SLC30A10 may be explained by reduced thyroxine production

SLC30A10 and SLC39A14 are manganese efflux and influx transporters, respectively. Loss-of-function mutations in genes encoding either transporter induce hereditary manganese toxicity. Patients have elevated manganese in the blood and brain and develop neurotoxicity. Liver manganese is increased in patients lacking SLC30A10 but not SLC39A14. These organ-specific changes in manganese were recently recapitulated in knockout mice. Surprisingly, Slc30a10 knockouts also had elevated thyroid manganese and developed hypothyroidism. To determine the mechanisms of manganese-induced hypothyroidism and understand how SLC30A10 and SLC39A14 cooperatively mediate manganese detoxification, here we produced Slc39a14 single and Slc30a10/Slc39a14 double knockout mice and compared their phenotypes with that of Slc30a10 single knockouts. Compared with wild-type controls, Slc39a14 single and Slc30a10/Slc39a14 double knockouts had higher manganese levels in the blood and brain but not in the liver. In contrast, Slc30a10 single knockouts had elevated manganese levels in the liver as well as in the blood and brain. Furthermore, SLC30A10 and SLC39A14 localized to the canalicular and basolateral domains of polarized hepatic cells, respectively. Thus, transport activities of both SLC39A14 and SLC30A10 are required for hepatic manganese excretion. Compared with Slc30a10 single knockouts, Slc39a14 single and Slc30a10/Slc39a14 double knockouts had lower thyroid manganese levels and normal thyroid function. Moreover, intrathyroid thyroxine levels of Slc30a10 single knockouts were lower than those of controls. Thus, the hypothyroidism phenotype of Slc30a10 single knockouts is induced by elevated thyroid manganese, which blocks thyroxine production. These findings provide new insights into the mechanisms of manganese detoxification and manganese-induced thyroid dysfunction.

Familial manganese-induced neurotoxicity due to mutations in SLC30A10 or SLC39A14

Over the last few years, two rare, familial diseases that lead to the onset of manganese (Mn)-induced neurotoxicity have been discovered. Loss-of-function mutations in SLC30A10, a Mn efflux transporter, or SLC39A14, a Mn influx transporter, increase Mn levels in blood and brain, and induce severe neurotoxicity. The discoveries of these genetic diseases have transformed our understanding of Mn homeostasis, detoxification, and neurotoxicity. Current knowledge about the mechanisms by which mutations in these transporters alter Mn homeostasis to induce human disease is reviewed here.

Zebrafish slc30a10 deficiency revealed a novel compensatory mechanism of Atp2c1 in maintaining manganese homeostasis

Recent studies found that mutations in the human SLC30A10 gene, which encodes a manganese (Mn) efflux transporter, are associated with hypermanganesemia with dystonia, polycythemia, and cirrhosis (HMDPC). However, the relationship between Mn metabolism and HMDPC is poorly understood, and no specific treatments are available for this disorder. Here, we generated two zebrafish slc30a10 mutant lines using the CRISPR/Cas9 system. Compared to wild-type animals, mutant adult animals developed significantly higher systemic Mn levels, and Mn accumulated in the brain and liver of mutant embryos in response to exogenous Mn. Interestingly, slc30a10 mutants developed neurological deficits in adulthood, as well as environmental Mn-induced manganism in the embryonic stage; moreover, mutant animals had impaired dopaminergic and GABAergic signaling. Finally, mutant animals developed steatosis, liver fibrosis, and polycythemia accompanied by increased epo expression. This phenotype was rescued partially by EDTA- CaNa₂ chelation therapy and iron supplementation. Interestingly, prior to the onset of slc30a10 expression, expressing ATP2C1 (ATPase secretory pathway Ca²⁺ transporting 1) protected mutant embryos from Mn exposure, suggesting a compensatory role for Atp2c1 in the absence of Slc30a10. Notably, expressing either wild-type or mutant forms of SLC30A10 was sufficient to inhibit the effect of ATP2C1 in response to Mn challenge in both zebrafish embryos and HeLa cells. These findings suggest that either activating ATP2C1 or restoring the Mn-induced trafficking of ATP2C1 can reduce Mn accumulation, providing a possible target for treating HMDPC.

Impaired function of the manganese transporter SLC30A10 has been implicated in HMDPC (hypermanganesemia with dystonia, polycythemia, and cirrhosis), an early-onset metabolic disorder clinically characterized by increased systemic Mn levels, neurological impairment, polycythemia, and hepatic injury. No specific treatment is currently available for HMDPC. Moreover, the mechanisms that underlie Mn metabolism are poorly understood, thereby hindering the development of effective treatments. To investigate the physiological processes underlying Mn metabolism and to develop new disease models of HMDPC, we generated two zebrafish slc30a10 mutant lines using the CRISPR/Cas9 system and found that these mutants develop clinical deficits typically associated with HMDPC. Furthermore, we identified a putative compensatory role for ATP2C1 in the absence of SLC30A10 with respect to modulating Mn metabolism. These findings provide a valuable tool for investigating the role of manganese dysregulation in neurological degenerative diseases and which can be used to develop new pharmacological approaches for managing Mn accumulation.

Deficiency in the manganese efflux transporter SLC30A10 induces severe hypothyroidism in mice

Manganese is an essential metal that becomes toxic at elevated levels. Loss-of-function mutations in SLC30A10, a cell-surface-localized manganese efflux transporter, cause a heritable manganese metabolism disorder resulting in elevated manganese levels and parkinsonian-like movement deficits. The underlying disease mechanisms are unclear; therefore, treatment is challenging. To understand the consequences of loss of SLC30A10 function at the organism level, we generated Slc30a10 knock-out mice. During early development, knock-outs were indistinguishable from controls. Surprisingly, however, after weaning and compared with controls, knock-out mice failed to gain weight, were smaller, and died prematurely (by ∼6-8 weeks of age). At 6 weeks, manganese levels in the brain, blood, and liver of the knock-outs were ∼20-60-fold higher than controls. Unexpectedly, histological analyses revealed that the brain and liver of the knock-outs were largely unaffected, but their thyroid exhibited extensive alterations. Because hypothyroidism leads to growth defects and premature death in mice, we assayed for changes in thyroid and pituitary hormones. At 6 weeks and compared with controls, the knock-outs had markedly reduced thyroxine levels (∼50-80%) and profoundly increased thyroid-stimulating hormone levels (∼800-1000-fold), indicating that Slc30a10 knock-out mice develop hypothyroidism. Importantly, a low-manganese diet produced lower tissue manganese levels in the knock-outs and rescued the phenotype, suggesting that manganese toxicity was the underlying cause. Our unanticipated discovery highlights the importance of determining the role of thyroid dysfunction in the onset and progression of manganese-induced disease and identifies Slc30a10 knock-out mice as a new model for studying thyroid biology.

N-oleoyldopamine modulates activity of midbrain dopaminergic neurons through multiple mechanisms

N-oleoyl-dopamine (OLDA) is an amide of dopamine and oleic acid, synthesized in catecholaminergic neurons. The present study investigates OLDA targets in midbrain dopaminergic (DA) neurons. Substantia Nigra compacta (SNc) DA neurons recorded in brain slices were excited by OLDA in wild type mice. In transient receptor potential vanilloid 1 (TRPV1) knockout (KO) mice, however, SNc DA neurons displayed sustained inhibition of firing. In the presence of the dopamine type 2 receptor (D2R) antagonist sulpiride or the dopamine transporter blocker nomifensine no such inhibition was observed. Under sulpiride OLDA slightly excited SNc DA neurons, an action abolished upon combined application of the cannabinoid1 and 2 receptor antagonists AM251 and AM630. In ventral tegmental area (VTA) DA neurons from TRPV1 KO mice a transient inhibition of firing by OLDA was observed. Thus OLDA modulates the firing of nigrostriatal DA neurons through interactions with TRPV1, cannabinoid receptors and dopamine uptake. These findings suggest further development of OLDA-like tandem molecules for the treatment of movement disorders including Parkinson's disease.

18F-FP-CIT dopamine transporter PET findings in cirrhotic patients with parkinsonism

We report the clinical features and imaging findings of presynaptic dopamine transporter (DAT) positron emission tomography (PET) in four of patients with liver cirrhosis and concurrent parkinsonism. We also reviewed previously reported cases of cirrhosis-related parkinsonism using dopaminergic molecular imaging. Our results using ¹⁸F-radiolabeled N-(3-fluoropropyl)-2β-carboxymethoxy-3β-(4-iodophenyl) nortropane (FP-CIT) DAT PET in four patients with cirrhosis and parkinsonism showed two different molecular imaging patterns well related to their neurological symptoms. ¹⁸F-FP-CIT PET imaging of two patients showed normal DAT density in the striatum. Their clinical features included symmetric parkinsonism, early gait disturbances and postural instability, and the absence of resting tremor. The other two patients showed reduced striatal DAT uptake asymmetrically with a rostrocaudal gradient similar to idiopathic Parkinson's disease (IPD). They had clinical findings of hemiparkinsonism, resting tremor, without early gait disturbance or postural instability. They also showed sustained response to levodopa treatment. Based on the structured review of 21 cases with cirrhosis-related parkinsonism in the literature including the present cases, we categorized cirrhotic parkinsonism into three groups. Eleven of the twenty-one cases were categorized into group 1; levodopa-resistant atypical parkinsonism without a dopaminergic deficit in molecular imaging similar to primary manganism. Another 6 cases were categorized into group 2; coincidental IPD with superimposed cirrhosis with sustained good response to levodopa and presynaptic dopaminergic deficit with rostrocaudal gradient typical of IPD. The other undetermined 4 cases were categorized into group 3. They showed symmetric parkinsonism with variable response to levodopa therapy. Their molecular imaging showed a global diffuse dopaminergic deficit in the presynaptic molecular imaging distinct to group 1 (normal uptake) or 2 (asymmetric rostrocaudal deficit). In conclusion, cirrhosis-related parkinsonism is a heterogeneous disorder.

Recent Updates on Acquired Hepatocerebral Degeneration

BACKGROUND

Acquired hepatocerebral degeneration (AHD) refers to a chronic neurological syndrome in patients with advanced hepatobiliary diseases. This comprehensive review focuses on the pathomechanism and neuroimaging findings in AHD.

METHODS

A PubMed search was performed using the terms "acquired hepatocerebral degeneration," "chronic hepatocerebral degeneration," "Non-Wilsonian hepatocerebral degeneration," "cirrhosis-related parkinsonism," and "manganese and liver disease."

RESULTS

Multiple mechanisms involving the accumulation of toxic substances such as ammonia or manganese and neuroinflammation may lead to widespread neurodegeneration in AHD. Clinical characteristics include movement disorders, mainly parkinsonism and ataxia-plus syndrome, as well as cognitive impairment with psychiatric features. Neuroimaging studies of AHD with parkinsonism show hyperintensity in the bilateral globus pallidus on T1-weighted magnetic resonance images, whereas molecular imaging of the presynaptic dopaminergic system shows variable findings. Ataxia-plus syndrome in AHD may demonstrate high-signal lesions in the middle cerebellar peduncles on T2-weighted images.

DISCUSSION

Future studies are needed to elucidate the exact pathomechanism and neuroimaging findings of this heterogeneous syndrome.

Inherited Disorders of Manganese Metabolism

While the neurotoxic effects of manganese were recognized in 1837, the first genetic disorder of manganese metabolism was described only in 2012 when homozygous mutations in SLC30A10 were reported to cause manganese-induced neurotoxicity. Two other genetic disorders of manganese metabolism have now been described - mutations in SLC39A14 cause manganese toxicity, while mutations in SLC39A8 cause manganese and zinc deficiency. Study of rare genetic disorders often provides unique insights into disease pathobiology, and the discoveries of these three inherited disorders of manganese metabolism are already transforming our understanding of manganese homeostasis, detoxification, and neurotoxicity. Here, we review the mechanisms by which mutations in SLC30A10, SLC39A14, and SLC39A8 impact manganese homeostasis to cause human disease.

Pathogenesis of hepatic encephalopathy in cirrhosis: the concept of synergism revisited

The concept of synergistic mechanisms as the pathophysiologic basis of hepatic encephalopathy started with the pioneering work of Les Zieve in Minneapolis some 60 years ago where synergistic actions of the liver-derived toxins ammonia, methanethiol, and octanoic acid were described. More recently, synergistic actions of ammonia and manganese, a toxic metal that is normally eliminated via the hepatobiliary route and shown to accumulate in brain in liver failure, on the glutamatergic neurotransmitter system were described. The current upsurge of interest in brain inflammation (neuroinflammation) in relation to the CNS complications of liver failure has added a third dimension to the synergy debate. The combined actions of ammonia, manganese and pro-inflammatory cytokines in brain in liver failure result in oxidative/nitrosative stress resulting from activation of glutamate (NMDA) receptors and consequent nitration of key brain proteins. One such protein, glutamine synthetase, the sole enzyme responsible for brain ammonia removal is nitrated and inactivated in brain in liver failure. Consequently, brain ammonia levels increase disproportionately resulting in alterations of brain excitability, impaired brain energy metabolism, encephalopathy and brain swelling. Experimental therapeutic approaches for which proof-of-principle has been established include the NMDA receptor antagonist memantine, N-acetyl cysteine (recently shown to have antioxidant properties at both hepatic and cerebral levels) and probiotics.

Structural and microstructral imaging of the brain in alcohol use disorders

Magnetic resonance imaging (MRI), by enabling rigorous in vivo study of the longitudinal, dynamic course of alcoholism through periods of drinking, sobriety, and relapse, has enabled characterization of the effects of chronic alcoholism on the brain in the human condition. Importantly, MRI has distinguished alcohol-related brain effects that are permanent versus those that are reversible with abstinence. In support of postmortem neuropathologic studies showing degeneration of white matter, MRI has shown a specific vulnerability of brain white matter to chronic alcohol exposure by demonstrating white-matter volume deficits, yet not leaving selective gray-matter structures unscathed. Diffusion tensor imaging (DTI), by permitting microstructural characterization of white matter, has extended MRI findings in alcoholics. This review focuses on MRI and DTI findings in common concomitants of alcoholism, including Wernicke's encephalopathy, Korsakoff's syndrome, hepatic encephalopathy, central pontine myelinolysis, alcoholic cerebellar degeneration, alcoholic dementia, and Marchiafava-Bignami disease as a framework for findings in so-called "uncomplicated alcoholism," and also covers findings in abstinence and relapse.

Exposure, epidemiology, and mechanism of the environmental toxicant manganese

It has become increasingly apparent that global manganese (Mn) pollution to air and water is a significant threat to human health. Despite this recognition, research is only beginning to comprehend the detrimental effects of exposure. Mn, while essential, is particularly harmful to the central nervous system, and overexposure is symptomatic of several neurological disorders. At-risk populations have been identified, but it is still unclear whether typical exposure levels have any long-term consequences. Those at an elevated risk have diminished intellectual function, learning and memory, and mental development. While the overall mechanism of toxicity is undetermined, Mn has been found to induce oxidative stress, exacerbate mitochondrial dysfunction, dysregulate autophagy, and promote apoptosis, ultimately enhancing neurodegeneration. Extrapolation of this in vitro and in vivo data to humans is difficult. There is a definite need to correlate epidemiological studies with causative effects. It is imperative that research efforts endure, so threats are appropriately identified and exposure properly regulated.

Management of Neurologic Manifestations in Patients with Liver Disease

OPINION STATEMENT

Liver disease, both in its acute and chronic forms, can be associated with a wide spectrum of neurologic manifestations, both central and peripheral, ranging in severity from subclinical changes to neurocritical conditions. Neurologists are frequently consulted to participate in their management. In this review, we present an overview of management strategies for patients with hepatic disease whose clinical course is complicated by neurologic manifestations. Type A hepatic encephalopathy (HE), which occurs in acute liver failure, is a neurologic emergency, and multiple measures should be taken to prevent and treat cerebral edema. In Type C HE, which occurs in chronic liver disease, management should be aimed at correcting precipitant factors and hyperammonemia. There is an increasing spectrum of drug treatments available to minimize ammonia toxicity. Acquired hepatocerebral degeneration is a rare complication of the chronic form of HE, with typical clinical and brain MRI findings, whose most effective treatment is liver transplantation. Epilepsy is frequent and of multifactorial cause in patients with hepatic disease, and careful considerations should be made regarding choice of the appropriate anti-epileptic drugs. Several mechanisms increase the risk of stroke in hepatic disease, but many of the drugs used to treat and prevent stroke are contraindicated in severe hepatic failure. Hepatitis C infection increases the risk of ischemic stroke. Hemorrhagic stroke is more frequent in patients with liver disease of alcoholic etiology. Viral hepatitis is associated with a wide range of immune-mediated complications, mostly in the peripheral nervous system, which respond to different types of immunomodulatory treatment. Several drugs used to treat hepatic disease, such as the classical and the new direct-acting antivirals, may have neurologic complications which in some cases preclude its continued use.

Structural Elements in the Transmembrane and Cytoplasmic Domains of the Metal Transporter SLC30A10 Are Required for Its Manganese Efflux Activity

Homozygous mutations in SLC30A10 lead to the development of familial manganese-induced parkinsonism. We previously demonstrated that SLC30A10 is a cell surface-localized manganese efflux transporter, and parkinsonism-causing mutations block its trafficking and efflux activity. Interestingly, other transporters in the SLC30 family mediate zinc efflux. Determining the mechanisms that allow SLC30A10 to transport manganese, which are unclear, is essential to understand its role in parkinsonism. Here, we generated a predicted structure of SLC30A10, based on the structure of the bacterial zinc transporter YiiP, and performed functional studies. In YiiP, side chains of residues Asp-45 and Asp-49 in the second and His-153 and Asp-157 in the fifth transmembrane segments coordinate zinc and are required for transport. In SLC30A10, the corresponding residues are Asn-43 and Asp-47 in the second and His-244 and Asp-248 in the fifth transmembrane segments. Surprisingly, although alanine substitution of Asp-248 abolished manganese efflux, that of Asn-43 and Asp-47 did not. Instead, side chains of charged or polar residues adjacent to Asp-248 in the first (Glu-25) or fourth (Asn-127) transmembrane segments were required. Further analyses revealed that residues His-333 and His-350 in the cytoplasmic C-terminal domain were required for full activity. However, the C-terminal domain failed to transfer manganese transport capability to a related zinc transporter. Overall, our results indicate that residues in the transmembrane and C-terminal domains together confer optimal manganese transport capability to SLC30A10 and suggest that the mechanism of ion coordination in the transmembrane domain of SLC30A10 may be substantially different from that in YiiP/other SLC30 proteins.

Movement Disorders in Non-Wilsonian Cirrhotic Patients: A Report of the Prevalence and Risk Factors from a Study Done in a Medical School in an Agricultural-Based Community

Objective

Parkinsonism and other movement disorders have previously been reported in the acquired hepatocerebral degeneration associated with portosystemic shunting. However, there is no study to date about their prevalence as has been noted in general practice.

Methods

One hundred and forty-three patients with hepatic cirrhosis from the gastroenterology clinic and internal medicine wards were enrolled. Liver data included the diagnoses, etiologies, assessments of complications, and treatments for cirrhosis. Hepatic encephalopathy was classified with regard to the West Haven criteria for semi-quantitative grading for mental status. Neurological examination results and abnormal involuntary movements were recorded as primary outcomes. Neuro-radiology was used for the detection of severe brain lesions.

Results

Alcoholism was the most common cause of liver cirrhosis. Eighty-three patients (58%) presented with movement disorders. Asterixis was found in one of the cases. The most common movement disorder seen was an intentional tremor at 37.1%, which was followed by bradykinesia, Parkinsonism, and postural tremors at 29.4%, 10.5%, and 6.3%, respectively. The prevalence of movement disorders simultaneously increased with a high Child-Turcotte-Pugh score. The hepatic encephalopathy was grade 1 and 2. With the inclusion of age-range adjustments, we found that alcoholic cirrhosis and hepatic encephalopathy are statistically significant factors [p < 0.05, odds ratio (OR) = 6.41, 95% confidence interval (CI) 1.38–29.71 and p < 0.001, OR = 13.65, 95% CI 4.71–39.54] for the development of movement disorders in non-Wilsonian cirrhotic patients.

Conclusions

Intentional tremor is a common abnormal movement. Alcoholic cirrhosis and hepatic encephalopathy are significant risk factors in the development of movement disorders in non-Wilsonian cirrhotic patients.

Nutrition in Chronic Liver Disease

Protein-calorie malnutrition is a transversal condition to all stages of chronic liver disease. Early recognition of micro or macronutrient deficiencies is essential, because the use of nutritional supplements reduces the risk of complications. The diet of patients with chronic liver disease is based on a standard diet with supplements addition as necessary. Restrictions may be harmful and should be individualized. Treatment management should aim to maintain an adequate protein and caloric intake and to correct nutrient deficiencies. The large majority of patients with grade I/II hepatic encephalopathy can tolerate a regular diet. Protein restriction can aggravate malnutrition and is not recommended, except in cases of hepatic encephalopathy unresponsive to optimized therapy.

Manganese homeostasis in the nervous system

Manganese (Mn) is an essential heavy metal that is naturally found in the environment. Daily intake through dietary sources provides the necessary amount required for several key physiological processes, including antioxidant defense, energy metabolism, immune function and others. However, overexposure from environmental sources can result in a condition known as manganism that features symptomatology similar to Parkinson's disease (PD). This disorder presents with debilitating motor and cognitive deficits that arise from a neurodegenerative process. In order to maintain a balance between its essentiality and neurotoxicity, several mechanisms exist to properly buffer cellular Mn levels. These include transporters involved in Mn uptake, and newly discovered Mn efflux mechanisms. This review will focus on current studies related to mechanisms underlying Mn import and export, primarily the Mn transporters, and their function and roles in Mn-induced neurotoxicity. Though and essential metal, overexposure to manganese may result in neurodegenerative disease analogous to Parkinson's disease. Manganese homeostasis is tightly regulated by transporters, including transmembrane importers (divalent metal transporter 1, transferrin and its receptor, zinc transporters ZIP8 and Zip14, dopamine transporter, calcium channels, choline transporters and citrate transporters) and exporters (ferroportin and SLC30A10), as well as the intracellular trafficking proteins (SPCA1 and ATP12A2). A manganese-specific sensor, GPP130, has been identified, which affords means for monitoring intracellular levels of this metal.

SLC30A10: A novel manganese transporter

Homozygous mutations in SLC30A10 cause familial parkinsonism associated with manganese (Mn) retention. We recently identified SLC30A10 to be a cell surface-localized Mn efflux transporter and demonstrated that parkinsonism-causing mutations block its intracellular trafficking and efflux function. In C. elegans, SLC30A10 over-expression protected against Mn-induced lethality and dopaminergic neurotoxicity, consistent with results in mammalian systems. Here, we present new data about SLC30A10 function in C. elegans. SLC30A10 expression did not protect worms against ZnSO4toxicity, suggesting that SLC30A10 does not mediate Zn export in C. elegans. Furthermore, while a blast search identified 5 potential SLC30A10 homologs in worms (cdf-1, cdf-2, ttm-1 and toc-1; sequence identity <35%), knock-down of these genes showed a tendency of increased survival after Mn exposure (although only ttm-1 was statistically significant), suggesting that the worm homologs may function differently.

Neurologic Manifestations of Chronic Liver Disease and Liver Cirrhosis

The normal functioning of brain is intimately as well as intricately interrelated with normal functioning of the liver. Liver plays a critical role of not only providing vital nutrients to the brain but also of detoxifying the splanchnic blood. Compromised liver function leads to insufficient detoxification thus allowing neurotoxins (such as ammonia, manganese, and other chemicals) to enter the cerebral circulation. In addition, portosystemic shunts, which are common accompaniments of advanced liver disease, facilitate free passage of neurotoxins into the cerebral circulation. The problem is compounded further by additional variables such as gastrointestinal tract bleeding, malnutrition, and concurrent renal failure, which are often associated with liver cirrhosis. Neurologic damage in chronic liver disease and liver cirrhosis seems to be multifactorial primarily attributable to the following: brain accumulation of ammonia, manganese, and lactate; altered permeability of the blood-brain barrier; recruitment of monocytes after microglial activation; and neuroinflammation, that is, direct effects of circulating systemic proinflammatory cytokines such as tumor necrosis factor, IL-1β, and IL-6. Radiologist should be aware of the conundrum of neurologic complications that can be encountered in liver disease, which include hepatic encephalopathy, hepatocerebral degeneration, hepatic myelopathy, cirrhosis-related parkinsonism, cerebral infections, hemorrhage, and osmotic demyelination. In addition, neurologic complications can be exclusive to certain disorders, for example, Wilson disease, alcoholism (Wernicke encephalopathy, alcoholic cerebellar degeneration, Marchiafava-Bignami disease, etc). Radiologist should be aware of their varied clinical presentation and radiological appearances as the diagnosis is not always straightforward.

Encephalopathy in Wilson disease: copper toxicity or liver failure?

Hepatic encephalopathy (HE) is a complex syndrome of neurological and psychiatric signs and symptoms that is caused by portosystemic venous shunting with or without liver disease irrespective of its etiology. The most common presentation of Wilson disease (WD) is liver disease and is frequently associated with a wide spectrum of neurological and psychiatric symptoms. The genetic defect in WD leads to copper accumulation in the liver and later in other organs including the brain. In a patient presenting with Wilsonian cirrhosis neuropsychiatric symptoms may be caused either by the metabolic consequences of liver failure or by copper toxicity. Thus, in clinical practice a precise diagnosis is a great challenge. Contrary to HE in neurological WD consciousness, is very rarely disturbed and pyramidal signs, myoclonus dominate. Asterixis and many other clinical symptoms may be present in both disease conditions and are quite similar. However details of neurological assessment as well as additional examinations could help in differential diagnosis.

Reprint of: Nutrition in the Management of Cirrhosis and its Neurological Complications

Malnutrition is a common feature of chronic liver diseases that is often associated with a poor prognosis including worsening of clinical outcome, neuropsychiatric complications as well as outcome following liver transplantation. Nutritional assessment in patients with cirrhosis is challenging owing to confounding factors related to liver failure. The objectives of nutritional intervention in cirrhotic patients are the support of liver regeneration, the prevention or correction of specific nutritional deficiencies and the prevention and/or treatment of the complications of liver disease per se and of liver transplantation. Nutritional recommendations target the optimal supply of adequate substrates related to requirements linked to energy, protein, carbohydrates, lipids, vitamins and minerals. Some issues relating to malnutrition in chronic liver disease remain to be addressed including the development of an appropriate well-validated nutritional assessment tool, the identification of mechanistic targets or therapy for sarcopenia, the development of nutritional recommendations for obese cirrhotic patients and liver-transplant recipients and the elucidation of the roles of vitamin A hepatotoxicity, as well as the impact of deficiencies in riboflavin and zinc on clinical outcomes. Early identification and treatment of malnutrition in chronic liver disease has the potential to lead to better disease outcome as well as prevention of the complications of chronic liver disease and improved transplant outcomes.

SLC30A10 is a cell surface-localized manganese efflux transporter, and parkinsonism-causing mutations block its intracellular trafficking and efflux activity

Manganese (Mn) is an essential metal, but elevated cellular levels are toxic and may lead to the development of an irreversible parkinsonian-like syndrome that has no treatment. Mn-induced parkinsonism generally occurs as a result of exposure to elevated Mn levels in occupational or environmental settings. Additionally, patients with compromised liver function attributable to diseases, such as cirrhosis, fail to excrete Mn and may develop Mn-induced parkinsonism in the absence of exposure to elevated Mn. Recently, a new form of familial parkinsonism was reported to occur as a result of mutations in SLC30A10. The cellular function of SLC30A10 and the mechanisms by which mutations in this protein cause parkinsonism are unclear. Here, using a combination of mechanistic and functional studies in cell culture, Caenorhabditis elegans, and primary midbrain neurons, we show that SLC30A10 is a cell surface-localized Mn efflux transporter that reduces cellular Mn levels and protects against Mn-induced toxicity. Importantly, mutations in SLC30A10 that cause familial parkinsonism blocked the ability of the transporter to traffic to the cell surface and to mediate Mn efflux. Although expression of disease-causing SLC30A10 mutations were not deleterious by themselves, neurons and worms expressing these mutants exhibited enhanced sensitivity to Mn toxicity. Our results provide novel insights into the mechanisms involved in the onset of a familial form of parkinsonism and highlight the possibility of using enhanced Mn efflux as a therapeutic strategy for the potential management of Mn-induced parkinsonism, including that occurring as a result of mutations in SLC30A10.

Nutrition in the management of cirrhosis and its neurological complications

Malnutrition is a common feature of chronic liver diseases that is often associated with a poor prognosis including worsening of clinical outcome, neuropsychiatric complications as well as outcome following liver transplantation. Nutritional assessment in patients with cirrhosis is challenging owing to confounding factors related to liver failure. The objectives of nutritional intervention in cirrhotic patients are the support of liver regeneration, the prevention or correction of specific nutritional deficiencies and the prevention and/or treatment of the complications of liver disease per se and of liver transplantation. Nutritional recommendations target the optimal supply of adequate substrates related to requirements linked to energy, protein, carbohydrates, lipids, vitamins and minerals. Some issues relating to malnutrition in chronic liver disease remain to be addressed including the development of an appropriate well-validated nutritional assessment tool, the identification of mechanistic targets or therapy for sarcopenia, the development of nutritional recommendations for obese cirrhotic patients and liver-transplant recipients and the elucidation of the roles of vitamin A hepatotoxicity, as well as the impact of deficiencies in riboflavin and zinc on clinical outcomes. Early identification and treatment of malnutrition in chronic liver disease has the potential to lead to better disease outcome as well as prevention of the complications of chronic liver disease and improved transplant outcomes.

Parkinsonian syndrome and ataxia as a presenting finding of acquired hepatocerebral degeneration

The term "acquired hepatocerebral degeneration" (AHD) was coined to describe clinical entity distinct from genetically defined Wilson's disease. AHD is chronic neurological disorder, characterized by extrapyramidal and neuropsychiatric symptoms accompanied with advanced liver disease with portosystemic shunts. In majority of AHD cases, extrapyramidal symptoms appear in the presence of known liver disease. Here we present a patient with subacute onset of bilateral, asymmetric, hypokinetic-rigid syndrome and ataxia as initial presentation of liver cirrhosis. Manganese toxicity have major role in AHD pathogenesis. Failure of liver detoxification and presence of portosystemic shunting enables neurotoxic substance of manganese to avoid hepatic metabolism and to enter and accumulate in central nervous system. Predilection brain regions for manganese deposits are globus pallidum (GP) and substantia nigra (SN). Characteristic MRI findings of bilateral, symmetrical hyperintensities of GP and SN on T1-weighted sequences supported the diagnosis of AHD in our patient. In addition, increased T2 signal in dendate nuclei seen in our patient is rare radiological finding. So far, no consensus guidelines regarding medical treatment of AHD exist. We initiated low-dose levodopa treatment, but failed to provide beneficial effect. In conclusion, AHD is distinct clinical entity that should be included in differential diagnosis of both typical and atypical parkinsonian syndromes. Furthermore, our case highlights the importance of performing MRI in patients with atypical parkinsonism.